Showing papers by "Iain R. Gibson published in 2003"

Calcium phosphate coatings obtained by Nd:YAG laser cladding: physicochemical and biologic properties.

Abstract: The plasma spray (PS) technique is the most popular method commercially in use to produce calcium phosphate (CaP) coatings to promote fixation and osteointegration of the cementless prosthesis. Nevertheless, PS has some disadvantages, such as the poor coating-to-substrate adhesion, low mechanical strength, and brittleness of the coating. In order to overcome the drawbacks of plasma spraying, we introduce in this work a new method to apply a CaP coating on a Ti alloy using a well-known technique in the metallurgical field: laser surface cladding. The physicochemical characterization of the coatings has been carried out by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). The biologic properties of the coatings have been assessed in vitro with human osteoblast-like MG-63 cells. The overall results of this study affirm that the Nd:YAG laser cladding technique is a promising method in the biomedical field.

In vitro degradation studies of calcium phosphate glass ceramics prepared by controlled crystallization

Abstract: Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K 2 O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca 2 P 2 O 7 (β-DCP), KCa(PO 3 ) 3 , β-Ca(PO 3 ) 2 and Ca 4 P 6 O 19 phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO 3 ) 3 phase, probably due to the presence of K + ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO 3 ) 3 , β-Ca 2 P 2 O 7 and β-Ca(PO 3 ) 2 phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates.

In vitro cellular response to titanium electrochemically coated with hydroxyapatite compared to titanium with three different levels of surface roughness

Abstract: The in vitro response of primary human osteoblast-like (HOB) cells to a novel hydroxyapatite (HA) coated titanium substrate, produced by a low temperature electrochemical method, was compared to three different titanium surfaces: as-machined, Al2O3-blasted, plasma-sprayed with titanium particles. HOB cells were cultured on different surfaces for 3, 7 and 14 days at 37 °C. The cell morphology was assessed using scanning electron microscopy (SEM). Cell growth and proliferation were assessed by the measurement of total cellular DNA and tritiated thymidine incorporation. Measurement of alkaline phosphatase (ALP) production was used as an indicator of the phenotype of the cultured HOB cells. After three days incubation, the electrochemically coated HA surface produced the highest level of cell proliferation, and the Al2O3-blasted surface the lowest. Interestingly, as the incubation time was increased to 7 days all surfaces produced a large drop in tritiated thymidine incorporation apart from the Al2O3-blasted surface, which showed a small increase. Cells cultured on all four surfaces showed an increased expression of ALP with increased incubation time, although there was not a statistically significant difference between surfaces at each time point. Typical osteoblast morphology was observed for cells cultured on all samples. The HA coated sample showed evidence of a deposited phase after three days of incubation, which was not observed on any other surface. Cells incubated on the HA coated substrate appeared to exhibit the highest number of cell processes attaching to the surface, which was indicative of optimal cell attachment. The crystalline HA coating, produced by a low temperature route, appeared to result in a more bioactive surface on the c.p. Ti substrate than was observed for the other three different Ti surfaces.

Comparison of Sintering and Mechanical Properties of Hydroxyapatite and Silicon-Substituted Hydroxyapatite

Abstract: Phase pure hydroxyapatite (HA), 0.8 wt.% silicon-substituted hydroxyapati te (0.8SiHA) and 1.5 wt.% silicon substituted hydroxyapatite (1.5SiHA) were isostatical ly pressed into discs and sintered between 900-1300 °C for 2 hours in order to assess the effect of silicon/carbonate cont nt on the density, microstructure, hardness and Young’s modulus of HA with sintering temperature. C-H-N chemical analysis of the as-prepared SiHA samples showed increa sed c rbonate absorption with silicon content compared to HA samples, but carbonate levels were not d tec ed when the samples were heat-treated. At low sintering temperatures (900-1000 °C) the densification of SiHA samples was inhibited, with this effect being more significant for the hig h level of silicon substitution (1.5SiHA) ceramics which was reflected in the hardness and Young’s modulus values of the ceramics. However, for high sintering temperatures (1200 and 1300 °C), the sintered densities, hardness and Young’s modulus of HA and SiHA were comparable. Furthermore, examina tion of the microstructures by scanning electron microscopy showed that silicon s ubstitution inhibited grain growth at high sintering temperatures. Introduction The similarities in the chemical composition of synthetic hydroxya patite (HA) and bone mineral has led to extensive use of HA ceramics as bone replacement materials. Alt hough bone bonds directly to the surface of HA, the number of medical applications of HA are li mited, primarily due to its relatively poor mechanical properties and slow rate of osseointegra tion compared to some other bioceramics [1]. A possible approach to improve the bioactivity of HA c eramics is to incorporate small levels of physiologically relevant ions into the HA lattic e. It has been shown that carbonate or silicon-substituted hydroxyapatite ceramics, exhibit enhanced in vitro [2,3] and in vivo [4,5] bioactivity compared to phase pure HA. Although these ionic substitutions e nhance the bioactivity of HA, studies have highlighted that the physical properties, such as t he degree of densification and sintered microstructure are affected with both the type and level of ionic substitution into HA. In particular carbonate substitution significantly reduces the sinteri ng temperature, required to achieve near-full density and equivalent grain size of the ceramic compare d to phase pure HA. However carbonate substituted hydroxyapatites are normally sintered in a moi st carbon dioxide environment which promotes densification [6]. Based on previous studies [6] on carbonate substituted HA, it is reasonable to assume that the substitution of silicon or silicate i ons into HA may also influence the densification and grain growth characteristics of the ceramic. T he aims of this study were, therefore, to determine the effect of silicon substitution and sintering temperature on t h mechanical properties of HA. Materials and Methods Phase pure hydroxyapatite (HA), 0.8 wt.% silicon-substituted hydroxyapati te (0.8SiHA) and 1.5 wt.% silicon-substituted hydroxyapatite (1.5SiHA) were prepared by aqueous precipitation reactions according to the methods described elsewhere [7]. The resulting preci pitate was filtered, dried at Key Engineering Materials Online: 2003-05-15 ISSN: 1662-9795, Vols. 240-242, pp 919-922 doi:10.4028/www.scientific.net/KEM.240-242.919 © 2003 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,21:21:03)